The invention relates to intraluminal endovascular stenting, and in particular, to a low profile fixed wire delivery catheter.
Endovascular stenting is particularly useful for arteries which are blocked or narrowed and is an alternative to surgical procedures that intend to bypass the occlusion. The procedure involves inserting a prosthesis into a body tube and expanding it to prevent collapse of a vessel wall. While stenting has most commonly been used adjunctively, following an intervention such as angioplasty or atherectomy, there is increasing interest in primary, or direct stent placement.
Percutaneous transluminal angioplasty (PTCA) is used to open coronary arteries which have been occluded by a build-up of cholesterol fats or atherosclerotic plaque. Typically, a guide catheter is inserted into a major artery in the groin and is passed to the heart, providing a conduit to the ostia of the coronary arteries from outside the body. A balloon catheter and guidewire are advanced through the guiding catheter and steered through the coronary vasculature to the site of therapy. The balloon at the distal end of the catheter is inflated, causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten re-closure of the dilated vessel or even perforations in the vessel wall. Implantation of a metal stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. Reducing the possibility of restenosis after angioplasty reduces the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
A stent is typically a cylindrically shaped device formed from wire(s) or a tube and is intended to act as a permanent prosthesis. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during an angioplasty procedure by using a balloon catheter bearing a compressed stent which has been loaded onto the balloon. The stent radially expands as the balloon is inflated, forcing the stent into contact with the body lumen thereby forming a supporting relationship with the vessel walls. Deployment is effected after the stent has been introduced percutaneously, transported transluminally and positioned at a desired location by means of the balloon catheter.
A balloon of appropriate size and pressure is first used to open the lesion. The process can be repeated with a stent loaded onto a balloon. Direct stenting involves simultaneously performing angioplasty and stent implantation using a stent mounted on a dilatation balloon. The stent remains as a permanent scaffold after the balloon is withdrawn. A balloon capable of withstanding relatively high inflation pressures may be preferable for stent deployment because the stent must be forced against the artery""s interior wall so that it will fully expand, thereby precluding the ends of the stent from hanging down into the channel, encouraging the formation of thrombus.
In adjunctive stenting, a stent delivery system with a small diameter profile is not required because the narrowing is already enlarged by the preceding device. However, in direct stenting, the stent and delivery balloon catheter need to be inserted into a stenosis that has not been previously dilated. Thus, for direct stenting to be applicable to many patients, the stent and delivery system must have a very low profile. The primary advantage of direct stenting is the procedural efficiency gained by eliminating a primary angioplasty step. The resulting procedure can be shorter and less expensive.
Primary angioplasty followed by stent placement typically requires a catheter exchange, which is usually performed over a guidewire. Given the prevalence of this staged procedure, the most commonly used balloon catheters have been over-the-wire types, having either a full length guidewire lumen or a short, distal guidewire lumen as found in rapid exchange catheters. Fixed wire, or xe2x80x9cballoon-on-a-wirexe2x80x9d type balloon catheters have been seldom used for primary angioplasty in stenting procedures, and these catheters have not been used to deliver stents at all. With their small size and wire-like trackability, fixed wire catheters are able to provide relatively quick and simple balloon placement and access to lesions that cannot be reached with other types of catheters. The small size of fixed wire catheters also permits their use through very small guiding catheters. However, these balloon catheters lack the ability to maintain guide wire position across a lesion and they may encounter problems re-crossing a dilated area. Thus, the present invention addresses these concerns to provide a fixed wire catheter suitable for direct stenting and accessing tortuous anatomy such as that found in the neurovascular.
The catheter of the present invention includes a wire-like metal shaft having a hollow portion defining a lumen extending therethrough. A core wire extends from a connection adjacent the distal end of the hollow portion. The connection includes multiple lateral crimps in the hollow portion, creating multiple lobes arranged around the core wire to provide communication with the lumen of the hollow portion. An elongate radiopaque tip spring is mounted to the distal tip of the core wire. A balloon is carried on the distal end of the shaft, but in a manner such that its distal end is unattached to the shaft thereby enabling the wire-like shaft to be rotated substantially independently of the balloon so that its rotation is not impaired. The proximal end of the balloon is attached to the distal end of an elongate outer tube, the proximal end of which is attached to the distal end of the hollow portion. The distal end of the balloon is attached adjacent the distal end of an inner tube, the proximal end of which is attached to and surrounds the core wire. The distal end of the inner tube extends distal to the balloon and surrounds the proximal end of the radiopaque tip spring. The balloon may be inflated and deflated through the lumen in the hollow portion, which communicates with the annular lumen defined between the outer and inner tubes.
In another embodiment of the invention, a compressed stent is mounted onto the deflated balloon of the fixed wire catheter.
An object of the invention is to provide an improved catheter and stent combination for low profile direct stenting.
Another object of the invention is to provide an improved catheter and stent combination for direct stenting in distal vascular anatomy.
Another object of the invention is to provide an improved catheter and stent combination for use through small diameter guiding catheters.
Another object of the invention is to provide an improved fixed-wire type balloon catheter.